Khilafah is defined as a general leadership system for all Muslims in the world to apply Islamic laws and carry the message of Islam to all parts of the world. The person who leads him is called the Caliph, can also be called Imam or Amirul Mukminin. For example, when his Caliph was Abu Bakr Ash-Shiddiq he was known as Khalifatu Ar-Rasulillah (his successor Prophet Muhammad), when Caliph Umar bin Khattab he was called Amirul Mukminin (leader of the believers), and when Caliph Ali bin Abi Talib he was called Imam Ali.
Khilafah comes from the word خلف (kha-la-fa), which means to replace. The definition of the Khilafah itself is a preposition of the word Khalifah. The word Caliph is taken based on the Qur'an surat Al-Baqarah verse 30.
In general, a system of government can be referred to as the Khilafah if it applies Islam as Ideology, sharia as the basis of law, and follows the leadership of the Prophet Muhammad and Khulafaur Rashidin in running the government, even with different naming or structure, but still adhere to the same principles, namely as the leadership authority of Muslims around the world. So that in its implementation, when a Khilafah State stands (with the consent of all Muslims), then the oath of allegiance of a Caliph, then the establishment of the Khilafah State and the bail of another Caliph after it becomes invalid. This is based on the hadith of the Prophet Muhammad about the caliphate.
In its history, the Caliph is a title given to the leaders of Muslims after the death of the Prophet Muhammad, namely with the nickname "Khulafaur Rashidin" or "Amir al-Mu'minin". Based on this nickname, the name of the Caliph was taken. So, the Caliph himself refers to the person who ruled or replaced the position of the Prophet Muhammad. While the Khilafah refers to the leadership system of the ummah, using Islam as an Ideology and its laws refer to the Qur'an, Hadith, Ijma and Qiyas.
The Khilafah system is a system applied in the early era of the development of Islam. In its history, after the death of the Prophet Muhammad, the companions pledged Abu Bakr to become Caliph. Then Abu Bakr died and his companions pledged allegiance to Umar bin Khattab. Then Umar bin Khattab died, the companions pledged allegiance to Uthman bin 'Affan.
Then Uthman ibn Affan died, the companions pledged allegiance to Ali ibn Abi Talib. Then such a system changed during the reign of the Umayyad Caliphate, the Abbasids, until the Ottoman period where after the Caliph died, he was replaced by his son. This system is similar to the system of government today. But what distinguishes it from the system of government is that the power of the Caliph is the power aimed at representing the people in governing and applying Islamic Sharia as the basis of law and government, while the power of the king is the absolute power that has full power to rule his country (Absolute Monarchy). symbolic which usually does not interfere in the affairs of government (Constitutional Monarchy).
